This invention relates to variable timing valve actuation systems for internal combustion engines, and more particularly to apparatus for controlling, adjusting, or modifying the intake and exhaust valve timing or other related characteristics by hydraulically linking the timings of intake and exhaust systems with high speed electromagnetic valves to achieve compression release retarding effects during every crank shaft revolution.
Concurrently filed, commonly assigned application Ser. No. 08/512,528 shows how lost motion in hydraulic linkages between engine cylinder valves and the mechanical inputs which normally control those valves can be selectively employed to modify the valve openings in relation to the normal inputs. These modifications can be of the timing or amount of valve openings, or the operating mode of the engine can be changed from positive power to compression release braking. However, if the engine is a four-cycle engine in positive power mode, it will also have four cycles in compression release engine braking mode. This means that it is only possible for each engine cylinder to produce one compression release event during every two revolutions of the engine crank shaft.
Sickler U.S. Pat. No. 4,572,114 shows apparatus for converting a four-cycle engine to two-cycle operation during compression release engine braking. This enables each engine cylinder to produce a compression release event during each revolution of the engine crank shaft, thereby approximately doubling the available compression release braking as compared to four-cycle braking. However, the Sickler apparatus is relatively complicated, employing, for example, two hydraulic connections (e.g., 136 and 212 in FIG. 5 or 258 and 212 in FIG. 7) to each valve opening mechanism.
In view of the foregoing, it is an object of this invention to improve and simplify the selective conversion of four-cycle engines to two-cycle compression release engine braking.
It is another object of this invention to extend the operating principles of the above-mentioned concurrently filed application to facilitate selective operation of a four-cycle engine in two-cycle compression release engine braking mode.